An investigation of antigens specific to six species of mycobacteria is being conducted. Filtrates of cultures grown on totally synthetic media have been prepared and subjected to immunochemical analysis. These filtrates have then been used to immunize goats for the preparation of homologous polyvalent antisera. Immunoabsorbents have been prepared from these antisera, and used to identify and isolate species specific antigens from these mycobacterial species in combination with physicochemical fractionation procedures. To date, an apparently specific highly anodal antigen from M. kansasii, designated Kll, has been isolated and characterized. Work has been initiated on the development of ELISA assays suitable for the identification of specific antigens of these mycobacteria which may be suitable for the rapid identification of these organisms in clinical specimens.